Thanks for your report. From your description, it seems that you are seeing the most recent update to the StumbleUpon extension for Chrome - you probably have your Chrome extensions set to 'auto-update'.
If you want to use it to Stumble, simply sign in, as you normally would. The Stumblebar can be moved to any part of the screen you prefer and 'docked'. It can also be adjusted in size and appearance. When in use, simply click on the StumbleUpon icon on your browser toolbar to make it disappear/reappear. As this is a very new release, we'd welcome your constructive feedback on how it works for you, should you decide to Stumble with it.
If you don't want to use it all, simply head over to your Chrome > Extensions menu and uninstall it.